src/pkg/testing/iotest/writer.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package iotest

import (
	"io";
	"os";
)

// TruncateWriter returns a Writer that writes to w
// but stops silently after n bytes.
func TruncateWriter(w io.Writer, n int64) io.Writer {
	return &truncateWriter{w, n};
}

type truncateWriter struct {
	w	io.Writer;
	n	int64;
}

func (t *truncateWriter) Write(p []byte) (n int, err os.Error) {
	if t.n <= 0 {
		return len(p), nil;
	}
	// real write
	n = len(p);
	if int64(n) > t.n {
		n = int(t.n);
	}
	n, err = t.w.Write(p[0:n]);
	t.n -= int64(n);
	if err == nil {
		n = len(p);
	}
	return;
}